[AKnowles]

Actually, that make perfect sense if the refridgerant all leaked out. Most cars, and I assume the Boxster too, run the compressor when the defroster is engaged so that in the cooler months the refridgerent and more importantly the lubricant gets a chance to be cycled and keep the o-rings and seals from drying out. If they dry out, you get a leak. Usually you need to replace the o-rings or seals to solve the problem and then refill it. A good tech shop can isolate the leak. You can too if you have a black-light and the right tools to refill your compressor and insert the dye. I've done it in the past, but nowadays I just take it to a specialist.